The prevalence of essential hypertension in black Americans is among the highest of any group in the world. The purpose of this research is to identify biological, behavioral, and social factors that influence heightened peripheral vascular reactivity in blacks -- a phenomenon that might place blacks at greater risk for hypertension. Of particular interest are two patterns of cardiovascular adjustment to stress frequently hypothesized to be related to hypertension: the beta-adrenergic "defense" pattern, characterized primarily by an increased heart rate, and the alpha- adrenergic "vasoconstriction" pattern, characterized primarily by an increase in vascular resistance. The latter pattern has been shown to be exaggerated in many blacks relative to their white counterparts. This project will explore biobehavioral and social factors that might contribute to a mediate this form of reactivity among blacks. Laboratory cardiovascular and neuroendocrine activity will be measured before, during, and after mental arithmetic (beta-adrenergic stressor), and the cold face stimulus (alpha-adrenergic stressor). In the three proposed studies using this paradigm, vascular and neuroendocrine reactivity will be examined as a function of resting blood pressure level, dietary sodium intake, and socioeconomic status. It is hypothesized that blacks who have borderline hypertension, who are on a high sodium diet, and have a low-income level will exhibit the greater alpha- adrenergic reactivity. These factors will also interact to further augment reactivity. In addition to the assessment of acute reactivity in the laboratory, assessments will also be made of chronic physiologic activity via ambulatory blood pressure monitoring and 24-hour urinary hormone excretion. These measures will also be examined as a function of the aforementioned risk factors. The proposed studies will document for the first time the relationships among race, dietary sodium, socioeconomic status, and blood pressure level on peripheral vascular and neuroendocrine stress reactivity and 24-hour ambulatory physiologic activity.